Lasers, particularly solid state lasers, have been used for years for recording and reading or sensing data on optical media. It has also been found that while reading from an optical disk of the rewriteable type, either reading data or sensing track crossings during a seek to a track operation, unintended partial or complete erasure occurs if the laser read power level is too high. Further, the operating parameters of media vary from one medium to the next; such variations are significant when using so-called removable optical media. It is desired to provide for enhanced read and seek operations while avoiding such inadvertent erasure.
A rotating disk has a lower linear speed at its inner diameter ID than at its outer diameter OD. As a result in the different speeds of scanning linearly along data tracks at different disk radii, using a constant laser power level results in greater heating and a higher temperature at the ID than the OD. Therefore the risk of inadvertent erasure at the disk ID is greater than at the disk OD. To accommodate this unintended data erasure exposure, it is a current practice to set read power levels at the ID. As a result of this read power level selection, the effective read power level at the OD is less than at the ID. It has been noticed by the inventors that such reduced effective read power level may result in a poorer quality read back signal. Accordingly, it is desired to provide a simple, yet reliable, method and apparatus for effecting improved read back from optical disks in areas remote from the ID while not having an unintended erasure exposure at the inner radii of the optical disk.